CVE-2026-20171 — The Border Gateway Protocol (BGP)&Nbsp;Enforce-First-As Feat Denial of Service
CVE-2026-20171 — A vulnerability in the Border Gateway Protocol (BGP) enforce-first-as feature of Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, remote attacker to trigger BGP peer flaps, resulting in a denial
What This Means For You
- If your environment is affected by CWE-670, review your exposure and prioritize patching based on your environment. Monitor vendor advisories for CVE-2026-20171 updates and patches.
Related ATT&CK Techniques
🛡️ Detection Rules
2 rules · 6 SIEM formats2 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
BGP Peer Flap due to Malformed BGP Update - CVE-2026-20171
title: BGP Peer Flap due to Malformed BGP Update - CVE-2026-20171
id: scw-2026-05-20-ai-1
status: experimental
level: critical
description: |
Detects BGP peer flaps on port 179, which is indicative of a denial of service condition caused by a malformed BGP update exploiting CVE-2026-20171. This rule specifically targets the BGP protocol (port 179) and the 'deny' action, suggesting a session termination or reset due to an invalid update.
author: SCW Feed Engine (AI-generated)
date: 2026-05-20
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-20171/
tags:
- attack.impact
- attack.t1499
logsource:
category: firewall
detection:
selection:
src_ip:
- '0.0.0.0/0'
dst_ip:
- '0.0.0.0/0'
dst_port:
- 179
action:
- 'deny'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-20171 | vulnerability | CVE-2026-20171 |
| CWE-670 | weakness | CWE-670 |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 20, 2026 at 20:16 UTC |
This content was curated and summarized by Shimi's Cyber World for informational purposes. It is not copied or republished in full. All intellectual property rights remain with the original author and source.
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